Pasko Rakic's research continues to focus on basic developmental mechanisms underlying the development of primate brain. As in the past year, the focus was on the role of clonal allocations of neurons to the cerebral cortex, the emergence of neurotransmitters and their receptors, the formation of synapses, and neuronal plasticity in the visual system of developing rhesus monkey, During 1995, this group published 10 full size papers that are fully, or in part, based on developing nonhuman primates obtained from the New England Regional Primate Research Center breeding colony. In studies which involve intrauterine surgery and cesarean sections, the surgical help of Dr. Prabhat Sehgal and his staff has been essential. For example, the injections of retrovirally-tagged probes to the cerebral vesicles of fetal macaque monkeys requires prenatal surgery which was carried out at the NERPRC. These complex studies are the first successful clonal analysis of the distribution of neurons in developing CNS carried out in any primate, and could not be achieved without the facilities and help of the NERPRC staff. In the next year (1996), we expect to use about 12 pregnant rhesus monkeys to carry out NIH